This invention relates generally to nanotube devices. More particularly, it relates to a nanotube sensors including chemical and biological sensors.
Sensing, chemical and biological species plays an important role in many industrial, agricultural, medical, and environmental processes. Detection of NO2 gas, for example, provides a crucial measure of environmental pollution due to combustion or automotive emissions. The amount of NH3 also needs to be closely monitored in industrial, medical and living environments. Moreover, there is a growing need to detect biological species in a variety of biomedical applications.
Chemical sensors in the prior art commonly employ solid state materials, such as semiconducting metal oxides, as sensing agents. The sensing is achieved by detecting change in electrical resistance of the sensor resulted from adsorption of foreign chemical species onto the sensing material. In order to achieve significant sensitivity, however, sensors of this type must operate at elevated temperatures so to enhance chemical reactivity. Other drawbacks of these prior art sensors include long recovery times (if not rendering irreversibility), poor reproducibility, and very limited range of chemical species each sensor is able to detect.
In view of the above, there is a need in the art for sensing devices that provide not only significant and robust, but more advantageously, tunable response to a variety of chemical and biological species.
The present invention is directed to versatile nanotube devices that are adapted for use in a variety of applications. In one example embodiment of the present invention, these nanotube devices are used in chemical and biological sensors. In another example embodiment of the present invention, individually separable nanotubes are grown in a controlled fashion. In another example embodiment of the present invention, nanotubes are manipulated and integrated into functional devices such as electrical, mechanical and electrochemical devices that can be individually tailored to a wide range of applications. In still another example embodiment of the present invention, nanotubes are modified so as to tune their sensitivity to a variety of molecular and/or biological species. Devices N which these nanotubes are used demonstrate significant and robust response.
A primary advantage of certain implementations of the present invention is that it provides a new class of electrical, mechanical, and electrochemical nanotube devices that can be individually tailored to a wide range of applications. Another aspect of the present invention involves implementations of the nanotube devices demonstrating significant and robust response, and more significantly, tunable selectivity to chemical or biologal species in their environments.
These and other advantages of various embodiments of the present invention will become more evident after consideration of the ensuing description and the accompanying drawings.
According to another example embodiment of the present invention, a device comprises a substrate and two catalyst islands disposed on the substrate. Each catalyst island is capable of growing nanotubes when exposed to a hydrocarbon gas at elevated temperatures. At least one nanotube forms between, with its two ends rooted in, the two opposing islands. Metal electrodes are then placed to fully cover the catalyst islands and the two ends of the bridging nanotube, providing means for measuring electrical response of the nanotube.
The substrate is typically made of doped silicon with a layer of native oxide. The catalyst comprises Fe2O3 and alumina nanoparticles. The catalytic island is typically about 3-5 microns in size. The nanotube is generally a single-walled carbon nanotube that can be semiconducting, or metallic. The metal electrodes typically comprise an alloy of nickel-gold, or titanium-gold.
The nanotube thus produced can be further modified by coating or decorating it with one or more sensing agents, such as metal particles, polymers, and biological species which impart sensitivity to a particular molecular species.
The selectivity of the nanotube to chemical species can also be tuned physically, for example, by applying a gating voltage to a nanotube. The gating voltage effectively shifts the Fermi energy level of the nanotube, giving rise to change in electrical conductivity of the nanotube upon adsorption of foreign chemical species.
In another example embodiment of the present invention, a device comprises a substrate covered with a layer of catalyst material. The catalyst enables the growth of nanotubes when exposed to a hydrocarbon gas at elevated temperatures, yielding a film of interconnected nanotubes disposed on the substrate. Two metal electrodes are then deposited onto the two opposing sides of the film, separated by a gap devoid of any metal. Such a nanotube film device can be easily produced in a scaled-up fashion with low cost.
The substrate in the above nanotube film device is typically made of quartz. The catalyst comprises Fe2O3 and alumina nanoparticles. The nanotubes are generally single-walled carbon nanotubes that are semiconducting, or metallic. The metal electrodes typically comprise an alloy of nickel-gold, or titanium-gold.
The nanotube film may further be modified by coating or decorating it with one or more sensing agents, so as to impart sensitivity to a particular species in its environment. The sensing agents include metal particles, polymers, and biological species.
The nanotube devices of the present invention demonstrate high sensitivity, robust response, and a tunable selectivity to a wide range of molecular species. They operate in gaseous and liquid environments.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments.